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TPS61099: Controlling the EN pin to avoid premature converter power-up

Chundra Ramful1
Prodigy 250 points
Part Number: TPS61099

Hello,

A few questions regarding page 7 of the data sheet:

(a) The maximum leakage current via the EN pin is 50nA at 5.0V.  Can we infer that the input impedance is 5 [V] / 50e-9 [A] = 5 [V] / 5e-8 [A] = 1e8 [Ohms]?

(b) I am designing the power circuitry for an energy harvesting application where the power input varies from 30uW to 300uW and I need to ensure that the boost converter remains OFF until the input supercapacitor voltage reaches1.2V.  Can a 10 MOhm pull-down (at the EN pin) ensure that the boost converter is not accidentally turned ON because of the leakage current via the EN pin?  I feel it should be fine but I am not sure how the converter will behave below a supply voltage of 1 V.  I would prefer to avoid the use of a 1MOhm pull-down to limit power loss during normal operation.

(c) Regarding V_IL for V_IN <= 1.5V, should the 0.2V x V_IN condition not be a maximum instead of a minimum?  Logically I would not want to exceed this condition to ensure a valid LOW at the EN pin.

(d) Regarding V_IH for V_IN <= 1.5V, should the 0.8V x V_IN condition not be a minimum instead of a maximum?  Logically I would not want to be below this condition to ensure a valid HIGH at the EN pin.

Your insight would be most appreciated.  Thank you,

Chundra

  • +1
    Prodigy 250 points

    Something I forgot to add regarding question (a) above...  Would this 1e8 Ohms input impedance (if valid) apply when the supply voltage to the converter is below the minimum of 0.7 V?

  • 0 in reply to Chundra Ramful1
    TI__Mastermind 27940 points

    Hi Chundra,

    Thanks for reaching out.

    For your questions, please see my comments below:

    (a) You can simply think it as a resistor. Actually, the pin is the input terminal of the internal comparator.

    (b) The leakage current into EN pin is sinking current, so you need to keep EN voltage below 0.2xVin so devices won't start up.

    (c) EN input low voltage threshold is the minimum value regarding Vin<=1.5V.

    (d) EN input high voltage threshold is the maximum value regarding Vin<=1.5V.

    By the way, The TPS61094 is a 60-nA IQ boost converter with supercap management. The device provides a power supply solution for smart meter and super capacitor backup power applications.

    Regards,

    Bryce